There have been many attempts to improve the efficiency of a bicycle's operation. One specific focus has been to improve the efficiency of the rider's motive power in order to effectuate an increased speed and a smoother fluctuation of the necessary cyclical movements.
Generally, efficiency is lost through the rotary motion of the rider's foot movements as the foot presses upon the pedal and crank assemblies at various stages of the rotary cycle. The maximum leverage is imparted by a foot when the pedal crank is at the forward horizontal position. Thus, in each rotary cycle there are two points in a full rotation of the crankshaft when the leverage imparted to the pedal crank is maximum. Conversely, in each rotary cycle there are two points when the leverage imparted to the pedal crank from the rider's foot is nil. This point of minimum leverage is developed when the pedal crank is at the vertical position. Sometimes the momentum of the system will carry the pedal crank once again into the forward horizontal position where leverage can again be exerted.
Sprocket wheels resiliently coupled to pedal crank drive systems are known. Most of these known mechanisms utilize torsional springs and, in particular, curved coupling springs for storing and releasing energy in the drive system. U.S. Pat. No. 4,753,127 incorporates this concept into the disclosed design.
However, because torsional springs are subject to the action of a bending moment, which produces a normal stress in the wire, they are most effective when the load is always applied so as to cause the spring to wind up.
Moreover, coupling springs are such that they can only exert the required spring force only if they are large in size, otherwise the energy released to the system will not be sufficient.
Alternatively, mechanisms are known which utilize translational springs. U.S. Pat. No. 2,316,530 crscioses using a translational spring for leverage compensation; however the design is such that it requires one large spring to transmit the needed power. Should the spring fail, the mechanism would be useless. In addition, a single spring does not balance the system whereas a plurality of springs located radially about the crankshaft will. A balanced system is important because it smoothes out the drive pedal fluctuations.
However, U.S. Pat. No. 4,468,207 discloses a plurality of translational springs interposed between two coaxial flywheels, but it does so for the purpose of damping the vibrations of the system.
While there have been prior attempts to store energy and then release it into the drive system at points of low leverage, there still exists a long felt need in the industry to correct cyclical fluctuations which rob the drive system of smoothness and continuous power.
Many of the known mechanisms for releasing energy into a drive system have the added disadvantage of not being easily adaptable to an ordinary bicycle and likewise not easily maintained by the user.